弓弦大梁
弓形横梁

Girder \Gird"er\, n. [From {Gird} to encircle.]
1. One who, or that which, girds.

2. (Arch. & Engin.) A main beam; a stright, horizontal beam
to span an opening or carry weight, such as ends of floor
beams, etc.; hence, a framed or built-up member
discharging the same office, technically called a compound
girder. See Illusts. of {Frame}, and {Doubleframed floor},
under {Double}.

{Bowstring girder}, {Box girder}, etc. See under {Bowstring},
{Box}, etc.

{Girder bridge}. See under {Bridge}.

{Lattice girder}, a girder consisting of longitudinal bars
united by diagonal crossing bars.

{Half-lattice girder}, a girder consisting of horizontal
upper and lower bars connected by a series of diagonal
bars sloping alternately in opposite directions so as to
divide the space between the bars into a series of
triangles. --Knight.

{Sandwich girder}, a girder consisting of two parallel wooden
beams, between which is an iron plate, the whole clamped
together by iron bolts.


Bowstring \Bow"string`\, n.
1. The string of a bow.

2. A string used by the Turks for strangling offenders.

{Bowstring bridge}, a bridge formed of an arch of timber or
iron, often braced, the thrust of which is resisted by a
tie forming a chord of the arch.

{Bowstring girder}, an arched beam strengthened by a tie
connecting its two ends.

{Bowstring hemp} (Bot.), the tenacious fiber of the
{Sanseviera Zeylanica}, growing in India and Africa, from
which bowstrings are made. --Balfour.